Various thermochemical processes have been proposed for producing hydrogen from water and create oxygen as a by-product. These thermochemical reactions have particular interest because of their potential use in connection with nuclear reactors and solar collectors which produce large quantities of fairly high-temperature heat. One such "water-splitting" process produces hydrogen iodide and sulfuric acid as a part of a closed-cycle chain of reactions and is disclosed in U.S. Pat. No. 4,089,940, issued May 16, 1978 to John H. Norman et al. This process is based upon the Bunsen equation whereby sulfur dioxide, water and iodine are reacted to produce sulfuric acid and hydrogen iodide. After the hydrogen iodide and the sulfuric acid are separated from the reaction mixture, the hydrogen iodide is decomposed to produce gaseous hydrogen and to recover iodine, which is returned to the main reaction. The sulfuric acid is decomposed to produce oxygen and to obtain sulfur dioxide and water which are returned to the main reaction.